2002 Highlander PO136 Error Code and Rough Idle

Usually in the exhaust pipe near the engine.
They don't usually cause a rough idle, and the check engine light should be on if you have a faulty sensor.

Poor idle rough. Poor exhilaration. Check engine light, sometimes bad exhaust smell

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When checking for Vacuum leaks, did you use a water spray bottle on seams and vacuum lines and EGR pod?(engine running)

Check for air leaks in exhaust before O2 sensors. O2 thinks its running lean from air leak in exhaust header and enrichens fuel charge.

Fuel injectors dirty, not closing tight. Switch injectors to other bank and see if Error Code moves to relocated injectors.

Bad spark plugs, check if you have fuel runners in your intake.

That's the symptom of a leaking head gasket. Is your coolant level low?

u reset the lite when u disconnected the battery. i would have the exhaust system checked asap!

Barring any mechanical issues you most likely have a failed injector.

Could be the Idle Control Valve?

before you do this I would get some wooden qtips - the long ones auto detailers use. take off the air filtrer assembly and spray carb cleaner into the air\fuel intake and use the qtip to wipe out the inside of the intake. I had the same problem with my highlander a year ago and this fixed the problem.

sounds like bad Idle Air control valve Not Cheap

check timing and set idle to 650rpm